In rotary internal combustion engines of the Wankel type, an exemplified in the Bentele et al U.S. Pat. No. 3,098,605, dated July 23, 1963, it is conventional to support a rotor for planetary rotary movement in a housing cavity on the eccentric portion of a mainshaft, a sleeve type bearing being carried by the rotor and dimensioned to be in close running fit with the peripheral surface of the eccentric portion of the mainshaft. To provide liquid lubricant to the interstices between the adjacent surfaces of the eccentric portion and the bearing, at least one annular channel is provided on the bearing surface adjacent the peripheral surface of the eccentric portion to receive liquid lubricant from at least one radially extending passageway in the eccentric, which passageway communicates the channel with a main supply passageway in the mainshaft, the main supply passageway receiving liquid lubricant under pressure from a suitable source thereof, as for example an oil pump.
In internal rotary combustion engines of the aforesaid type which are of large size, as for example 350 cubic inch displacement, it has been found that the aforesaid conventional method or system for lubricating the rotor bearing, was unsatisfactory since such bearings overheated and structurally failed. More specifically, it was found that the vector sums of the combustion gas pressures and the centripetal forces of the rotor acting on the eccentric portion of the mainshaft exceeded the load carrying capacity of the bearing by reducing the lubrication film thickness in the interstices between the bearing and eccentric portion of the mainshaft to the point that those surfaces came in direct contact and thus caused overheating and failure of the bearing. Since space limitations prevented the widening of the bearing to increase its load carrying capacity, such an approach was not a solution to the problem. In another unsatisfactory solution, flats were provided in the eccentric surface at the discharge end portions of the radially extending lubrication supply passageways to facilitate distribution of the lubricant over the bearing surface. This proved unsatisfactory because it actually reduced lubricant flow and caused higher temperature rises hence exacerbating the problem. A further unsatisfactory suggestion for solving the problem was to increase the clearance between the bearing and eccentric portion of the mainshaft. This, however, was undesirable because it had the effect of reducing the minimum backlash in the rotor timing gears and could cause contact of the apex portion of the rotor with the rotor housing. A partial solution to the problem is disclosed in West Germany Offenlegungsschrift patent No. 2062219 which issued June 22, 1972. In this patent, an arcuate channel of 90.degree. in length is provided in the surface of the eccentric portion of the mainshaft in the zone of least centripetal force on the eccentric portion of the mainshaft, the arcuate channel starting 30.degree. after an imaginary radial line extending through the point of maximum throw of the eccentric. Two radially extending lubricant supply passages are provided to conduct lubricant from a main supply passageway in the mainshaft to spaced points in the channel. This solution of delivering the lubricant to the area of greatest spacing between the bearing and eccentric portion agreed with applicant's finding that centripetal forces were of greater significance in connection with lubrication of the rotor bearing than the combustion gas pressure forces on the eccentric portion of the mainshaft at high engine rpm, e.g. 3600 rpm. However, the rotor bearing lubricating system disclosed in the aforesaid Offenlegunsschrift patent, is only a partial solution to the rotor bearing lubrication problem because, while it achieves satisfactory distribution of lubricant at high rpm where combustion gas pressures, e.g. 650 psi, are substantially offset by the centripetal forces, it fails to provide the desired distribution of lubricant when the engine is operating at low rpm, e.g. 900 rpm, and under a "lugging" condition or mode. The word "lugging" is to be understood to mean an operating condition or mode where the engine is under high power (throttle wide open) but the engine rpm is low. Under a lugging condition graphically shown in FIG. 5 hereof, the centripetal forces on the eccentric portion are relatively weak and the combustion gas pressures are relatively high and become of significance so that the resultant or mean force on the eccentric portion of the mainshaft is in the general direction of the line of the greatest throw of the eccentric portion instead of on a line generally normal thereto. Under the lugging operative condition, the channel of the rotor bearing lubricating system disclosed in the West German Offenlegungsschrift patent does not provide the desired film of oil between the bearing and eccentric portion of the mainshaft.
Accordingly, it is an object of this invention to provide, in a Wankel type rotary internal combustion engine, a rotor bearing lubrication system which is effective during all operating conditions of the engine to provide the desired distribution of lubricant to the interstices between the eccentric portion of the mainshaft and the surrounding bearing.
It is another object of the present invention to provide, in a Wankel type rotary internal combustion engine, a rotor bearing lubricating system wherein lubricant is effectively distributed to the interstices between the bearing and rotor journal when the engine is in a lugging mode of operation.